1. Field of the Invention
The invention relates to protective wear. More specifically the invention relates to flexible body armor designed to defeat high velocity fragmentation projectiles.
2. Background
In recent years fragment resistant materials formed from high tensile strength fibers such as aramid fibers or polyethylene fibers, have gone into common use in the field. Unfortunately, soft body armor, even with these advanced materials, have proven insufficient to thwart armor piercing pistol ammunition, sharp thrusting instruments, and circular penetrators, all which are now in common use.
To address this problem, various hard metal plating systems have been developed. One attempt to shield soft targets from fragmentation involves the use of approximately 1xe2x80x3xc3x9712xe2x80x3 large hard plates attached to a vest type garment. The difficulty with this approach is that the vest is bulky, difficult to move around in and heavy. Another attempt is using smaller rigid plates aligned with metal and/or ceramic overlapping edges. However, these vests are cumbersome as well and are not sufficiently flexible.
Another such solution employs a number of titanium disks one inch in diameter and having uniform thickness in the range of 0.032 to 0.050 inches in thickness laid out in overlapping rows such that the interior of a row, a disk overlaps its predecessor in the row and is overlapped by its successor in the row. Subsequent rows overlap the predecessor and are overlapped their successor. The coin layout is then attached to a substrate such as an adhesive impregnated aramid fabric. A second layer of adhesive impregnated aramid fabric may be used to envelop the xe2x80x9cpanelxe2x80x9d formed by the coins. This enveloped panel can be attached to conventional soft body armor over vital organ area of the torso. It provides good flexibility and is thin enough to conceal. A third solution employs a number of high hardness plates often of a hexagonal shape. Such plates typically have a uniform thickness in the range of 0.032 to 0.050 inches and are tiled over the area to be protected.
Fragmentation artillery rounds contain an explosive charge designed to distribute fragmentation and shrapnel which are metal projectiles arrayed around the explosive charge contained in a metal encasement wall that on detonation of the explosive charge fragments into irregular shaped hot high velocity projectiles. After detonation, the artillery projectile encasement wall is torn to shreds and becomes fragments. Fragmentation and shrapnel wounds are caused when these hot jagged pieces of steel are impelled away from the sight of the explosion and by virtue of their velocity and mass tear into and destroy soft targets, for example, people. The above mentioned overlapping of coins have been shown to spread the force effectively of a pistol round protecting a wearer from handgun injuries. However, these vests still do not fully resist penetration enough to protect the wearer from high velocity and mass fragmentation effects of a shrapnel artillery round.
The damage done by fragmentation is usually modeled using a bullet type sabot fragment simulator. One such simulator is a right round circular penetrator. These are solid steel projectiles with blunt ends about 0.217xe2x80x3 in diameter and 0.220xe2x80x3 in length. Another simulator is the stanag 2920 NATO standard which has a chisel point, weighs about 17 grain, has a velocity of 650 meters per second, and is 0.217xe2x80x3 in diameter and 0.260xe2x80x3 in length. One level of fragmentation protection provided by armor has been quantified in U. S. military standard (mil std) 662E. A xe2x80x9cF6xe2x80x9d fragmentation level of protection, as defined by mil std 662E, will stop a stanag 2920 projectile traveling at 650 meters per second generating at least 20.53 foot pounds of energy. This is the highest body armor fragmentation velocity standard in use.
The damage done by fragmentation and/or shrapnel can be modeled using armor piercing bullets as well. The results from armor piercing bullet emulations can provide an indication of general fragmentation stopping ability of a vest. An examination of the encasement wall of the artillery round properties (i.e. type of steel, thickness of encasement wall, diameter of artillery round), along with characterization of the explosive charge (i.e. composition and amount of powder) permits deductions about fragment size generated by a detonation, for example mass and volume of fragments, from a shrapnel shell. Also the above analysis gives a good indication of fragment velocity at the location of the detonation. Analysis of intended burst altitudes of the shell along with mechanics allows an estimation of fragment velocity at impact of a typical target. Armor piercing bullets are used, because they have not been designed, like for example hollow point bullets, to deform on impact and therefore more closely resemble fragments on impact.